Researchers at Duke University studied Japetella heathi, a short armed, seven centimeter long octopus and Onychoteuthis banksii, a 12 centimeter long squid, both found at depths of 600-1000 meters.
These species are mostly transparent, which protects them from silhouette-spotting predators. Transparency doesn’t protect them from “headlight fish,” because the eyes and guts of the cephalapods reflect light.
Researchers found that when exposed to bluish light, like the light from headlight fish, the octopi and squid turn red, making them appear less reflective. Once the light was removed, they turn transparent once again.